Polyacetal polymers, which are commonly referred to as polyoxymethylene polymers, have become established as exceptionally useful engineering materials in a variety of applications. Polyoxymethylene polymers, for instance, are widely used in constructing molded parts, such as parts for use in the automotive industry and the electrical industry. Polyoxymethylene polymers have excellent mechanical properties, fatigue resistance, abrasion resistance, and chemical resistance.
Although polyoxymethylene polymers have excellent physical characteristics, the polymers may not be suitable components in certain applications, such as in fuel transfer applications, where the risk of a spark or explosion is increased. Because the electrical resistances within plastics such as polyoxymethylene are usually very high, there is a risk of electrostatic charging, which can be disruptive and even dangerous in certain application sectors, such as in the fuel and automotive sectors. This risk is due to the inability of the polymers to dissipate electrical charge. For instance, unlike metallic components, which provide an electrical pathway for electrical charges to move freely to ground, when a non-conductive, plastic component is used, such a pathway is removed, leaving no way for charges to drain to ground. This, in turn, creates a risk of sparking or explosion when a plastic component is used. As such, conductive fillers including metal fibers such as metal fibers or electro-conductive (EC) carbon black can be added to polyoxymethylene to impart the polyoxymethylene with electrostatic dissipative (ESD) capabilities. However, although the addition of such fillers can improve the electrical conductivity of the polyoxymethylene, the amount of conductivity across an article formed from the ESD polyoxymethylene can be highly variable due to molding conditions and the inability to regulate the precise distribution of the conductive fillers within the polyoxymethylene resin. This can result in supposedly ESD capable polyoxymethylenes inadequately dissipating charge when needed.
Further, standard polyoxymethylene polymers may be susceptible to degradation when exposed to aggressive fuels. For instance, diesel fuel can age at high temperatures, resulting in a damaging effect on polyoxymethylene due to the oxidation of sulfur or sulfur-containing compounds. This, in turn, reduces the toughness (i.e., strain at break) of the polyoxymethylene. Further, gasoline fuels can have a degrading effect on polyoxymethylene as such fuels generally have an acidic and oxidative nature that, like diesel fuels, can also damage polyoxymethylene.
In view of the above, a need exists for a polyoxymethylene polymer composition that has improved electrostatic dissipative (ESD) capabilities and is resistant to degradation upon exposure to aggressive fuels, as well as articles formed from such a composition.